Snap action electric switch



April 19, 1949. R. s. LEES-ANDREWS SNAP ACTON ELECTRIC SWITCH Filedneo. 1o, 194e y? l i Patented Apr. 19, 1949 SNAP ACTION ELECTRIC SWITCH Robert Samuel Lees-Andrews, Cheltenham, England, asslgnor to Bisset Industries Limited, Cheltenham, England, a company of Great Britain Application December 10, 1946, Serial No. 715,189

Inv Great Britain April 8, 1946 6 Claims.

This invention relates to snap action electric switches of the kind (hereinafter referred to as the kind described) in which a resilient strip or blade co-operates with a xed contact or contacts to make or break an electric circuit and is pre-stressed to take up one or other of two limit positions on either side of a dead-centre position in which it is in unstable equilibrium.

It is an object of this invention to provide a switch of the kind described which is simple in construction and reliable in operation.

The present invention provides a snap action switch which when operated into the closed position will remain in this position until positively operated into the open position.

The nature of the invention will 'be more clearly understood from the following description, given by way of example, of one embodiment constructed in accordance therewith and illustrated in the accompanying drawings, in which- Fig. 1 is an exploded perspective view of a change-over switch,

Fig. 2 is a longitudinal section of the switch shown in Fig. 1, with the moving parts in one operated position,

Fig. 3 is a side elevation with part of the housing broken away and with the moving parts in the other operated position, and

Fig. 4 is an end elevation seen in the direction of the arrow IV of Fig. 3, some parts being removed.

The switch illustrated is of the push button type and consists of a hollow rectangular oiltight box or body part l forming a housing for the moving parts of the switch. The body part I is closed in an oil-tight manner by an insulating carrier plate 2 rigidly secured thereto as by cementing or by screws with the interposition of an oil-seal washer or gasket l a, and an escutcheon plate 3 is secured to the front of the carrier plate 2 to give a nished and suitably decorative appearance. Alternatively, the escutcheon plate may be replaced by a switch cover having button shrouds to conform to the appropriate regulations when the switch is to be used for industrial purposes.

The cover may be made of an aluminium alloy, and the box or body part I may then be a die-cast case with a conduit entry boss. 'Ihe carrier plate 2 is divided into two parts 2a, 2b to accommodate oil seals I3 around the switchoperating rods, as will be described more fully below. On the carrier plate 2 are mounted two pairs of contacts 4, 5, the pair of contacts 4 being mounted in a plane spaced slightly behind that of the pair of contacts 5. The two pairs of contacts are arranged on either side of the transverse centre-line C (Fig. 4) and are connected by rigid strips 4a, 5a, respectively, to the terminal pillars 4b, 5b. At one end of the carrier plate 2 is mounted a U-shaped anchor member 6, the limbs of the U being of the same height. The two limbs of the U are cut away for part of their width, the lower limb-as seen in Figs. 1 and 2-being cut away at its centre to present a pair of abutments 'l which are grooved transversely on their upper faces near the free ends to receive the lower end of an H-shaped resilient blade 8 of silver-faced beryllium copper. The upper limb 9 of the U- shaped anchor member 6 is cut away along each side to enable it to project with clearance between the sides of the H-shaped resilient blade, and is transversely grooved on its under surface near the outer end thereof to constitute a fixed fulcrum part. 'I'his fulcrum part 9 is engageable by a forward projection Illa on an operating member or lever i0 of approximately the same overall dimensions as the resilient blade 8. This forward projection 9 has a knife-edge formation at its extremity which seats in the groove in the xed', iulcrum part 9, the combination acting as a substantially frictionless fulcrum for the operating lever l0.

The lower end of the operating lever Ill has an inturned lug Ib which passes between the two halves of the lower blade abutment l. The upperv end of the lever l0 has an inturned abutment lug |00, the under surface of which is grooved near its free end to receive the upper ends of the resilient blade 8. The arrangement and dimensions of these parts are such that, when the blade is mounted in the grooves in its upper end lower abutments |00, l, respectively, it must flex Slightly under endwise pressure to enable the fulcrum projection Illa of the operating lever I 0 to enter the complementary groove in the xed fulcrum part 9. The stress thus set up in the resilient blade 8 holds the fulcrum in engagement, and at the same time operates to bias the blade to a ilexed contour on one or other side of a dead-centre position in which it is in unstable equilibrium. The xed contacts 4, 5 on either side of this dead centre position dene the limit positions of this ilexure.

The cross-piece 8a of the resilient blade 8 is Y,

arranged to bridge the pairs of fixed contacts 4 or 5 and so to close the respective external circuit. To operate the switch, the operating lever III is tilted, rocking it about its fulcrum 9, Illa and initially pressing the blade against the made" contacts (l in Fig. 1), so as to tend to straighten it, until it passes through its dead centre position and snaps over to come to rest, in its other limit position, to bridge the other pair of contacts 6.

For moving the operating lever I0, two insulating push-buttons II are mounted on stems I2 which pass through the carrier plate 2 and the escutcheon plate 3, the part 2b being recessed on its undersurface around the holes for the stems I2 to receive packing washers I3. The housing I is lled to the required level with transformer oil, thereby increasing the current breaking capacity of the switch, or conversely reducing the overall size of the switch for a given circuit. The buttons Il may be distinctively coloured or engraved to indicate the setting of the switch. The housing is secured in position by means of a cruciform fixing frame I4 screwed thereto at I5, the arms Ma having iixing holes I 6 drilled therein. The frame I4 may be crimped during installation of the switch in order to allow the sealing face of the escutcheon plate to be located parallel with the plane of the outer surface of the wall or other support on which the switch is being installed.

In a modied construction, the resilient blade 8 may constitute one contact, to co-operate with a single xed contact or contacts connected to the other part or parts of the external circuit.

A plurality of switch units may be mounted side by side on a common carrier plate and in a common body or housing, each unit having its oWn set of fixed contacts such as 4, andiresilient blade such as 8. A common escutcheon plate may be used, and may be engraved so as to identify the several circuits.

The design described above, which is not limitative of the invention as to details of construction, is lsimple to manufacture and assemble since all the working parts may be stamped out by a simple press-tool or like operations, The body I, carrier plate 2 and escutcheon plate 3 may be plastic mouldings or they may be metal castings or forgings, or may be fabricated from sheet metal. Furthermore, the fuicrum arrangement 9, Illa is sturdy, and by reason of the knife-edge feature of construction at all points where relative motion occurs, friction is reduced to a minimum, thus adding to the sensitivity and reliability of operation of the switch, even under adverse climatic conditions. Instead of being mounted in or on a carrier plate 2, the iixed parts of the switch may be mounted on a rigid frame work constituting the carrier part which may be enclosed by any desired form of sheeting, or may be incorporated into a larger assembly of components.

If desired, all the parts, with the exception of the fixed contacts and the resilient blade, may be of moulded plastic materials, although even the blade may be of a plastic or other tough and :flex-y ible insulating material if desired. In the latter case, the cross-piece of the H-shaped blade 8 may be of metal. In this case also, the resilient blade s may have more than one cross-piece such as 8a, each cross-piece co-operating with respective xed contacts for controlling simultaneously a plurality ofcircuits. By this means insulating and corrosion difficulties can be reduced to a minimum.

The switch is capable of many applications, particularly to the control of low-power domestic or industrial circuits.

What I claim is:

l. A snap action electric switch comprising a carrier plate, a ixed abutment extending from said carrier plate. a rigid, movable switch operating member having an abutment at one of its ends spaced from said xed abutment, a resilient blade carried at its ends in said abutments and having a length greater than the distance between the fixed abutment and the abutment on the switch operating member, said resilient blade being movable with the switch operating member about said xed abutment as a pivot, a second iixed abutment extending from the carrier plate intermediate said iirst fixed abutment and said abutment on said switch operating member, said switch operating member and said second iixed abutment being provided with separate rigid inter-engaging pivot formations so that the ends of said rigid switch operating member including said abutment thereon move along an arcuate path of shorter radius than that which would be described by said resilient blade if unrestrained, spaced stop members on each side of said resilient blade, at least one of said stop members constituting a fixed contact of the switch, and means for moving the switch operating member and corespondlngly moving said resilient blade from one extreme position in which the resilient blade engages one stop and is curved convexly toward the carrier plate to another extreme position in which the resilient blade engages the other of said stops and is curved concavely toward the carrier plate.

2. A snap action electric switch comprising a carrier plate, a xed abutment mounted on the carrier plate towards one end thereof, a rigid switch operating member, separate rigid interengaging pivot formations on the switch operating member and the carrier plate, that on the latter being at a point nearer the other end of the carrier plate than the fixed abutment, an abutment on the switch operating member distant from the xed abutment, a rst stop mounted on the carrier plate between the xed abutment and the abutment on the switch operating member, a second stop mounted on the carrier plate at a point between the fixed abutment and the abutment on the switch operating member and spaced from the rst stop, at least one of said stops consistuting a xed contact of the switch, a resilient blade carried at its ends in the fixed abutment and the abutment on the switch operating member and extending through the gap between the two stops and of a length greater than the distance between the xed abutment and the abutment on the switch-operating member at all positions, and extending from the abutment on the switch operating member beyond the pivot point of the switch operating member to the fixed abutment, andvmeans for moving the switch operating member from one extreme position in which the resilient blade engages one stop and is curved convexly towards the carrier plate to another extreme position in which the resilient blade engages the other stop and is curved concavely towards the carrier plate.

3. A snap action electric switch as set forth in claim 2 wherein the rigidpivot formation on the carrier plate and the xed abutment are formed facing each other on opposite limbs of a U-shaped member secured to the carrier plate.

4. A snap action electric switch as set forth in claim 3 wherein the rigid switch operating member is pivoted at a point between the fixed alternatar abutment and the median point of the resilient blade.

5. A snap action electric switch according to claim 2 wherein the means for moving the switch operating member includes two plungers projecting through the carrier plate and operatively engaged with the switch operating member on each side of the inter-engaging pivot formations and wherein the resilient blade is of H shape with the plungers extending therethrough.

6. A snap action electric switch comprising a carrier plate, a xed abutment mounted on the carrier plate towards one end thereof, a rig-id switch operating member, an abutment on the switch operating member distant from the xed abutment, a first stop mounted on the carrier plate between the fixed abutment and the abutment on the switch operating member, a second stop mounted on the carrier plate at a point between the fixed abutment and the abutment on the switch operating member and spaced from the first stop, at least one of said'stops constituting a fixed contact of the switch, a resilient blade carried at its ends in the fixed abutment and the abutment on the switch operating member and extending through the gap between the two stops and of a length greater than the distance between the xed abutment and the abutment on the switch operating member at all positions, separate rigid inter-engaging pivot formations on the switch operating member and the carrier plate, the point of engagement being between the xed abutment and the median point of the resilient blade, which extends from the abutment on the switch operating memberbeyond the pivot point of the switch operating member to the fixed abutment, and means for moving the switch operating member from 'one extreme position in which the resilient blade engages one stop and is curved convexly towards the carrier plate to another extreme position in which the resilient blade engages the other stop and is curved concavely towards the carrier plate.

ROBERT SAMUEL LEES-ANDREWS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATEy 5 PATENTS 

